Introduction to Astronomy (I)

What is Astronomy?

Astronomy, as we will apply the term in this class, is the scientific study of the physical Universe, the rich variety of objects that populate it, and the processes that take place within and between these objects. (Earth, in this context, is a valid object of study to the extent we think of it as a particularly accessible example of a class of objects - terrestrial planets.) By some traditional definitions, we are blurring the distinction between Astronomy and Astrophysics.

Astronomy is one of the oldest sciences, with a rich history. It is also an exciting frontier of knowledge as our understanding of the cosmos is changed by new observations and theoretical advances. To me, as a physicist, the most thrilling aspect of the field is the extent to which humans have been able to understand our Universe.

I should pause here to clarify that in the context of physical science, the term “understand” has a very specific meaning. What we seek is a set of universal laws governing the Universe. These express our understanding in terms of mathematical relations between measurable physical properties of the objects of study. These relations can then be compared to the results of actual measurements (in Astronomy these are often called observations but don’t let the word fool you).

What this means for our class is that to the extent this is possible we will try to understand the amazing variety of phenomena the universe presents. Wherever possible, we will try to produce simplified, idealized versions of the calculations made by professionals, such that they are possible with finite effort at the level of mathematics this course requires: a working knowledge of high-school level algebra. Sometimes we will not manage to do this and will have to satisfy ourselves with waving our hands and telling a story. Hopefully you will find that while fun, this falls far short of the joy of really doing it, and be motivated to go deeper soon. At other times, our insight relies on complex combinations of detailed equations and numerical simulations, so we will just show the results.

Our understanding of the Universe, in this sense, is an incremental process in which we come up with successively closer approximations to the truth. Technically, this means our calculations are increasingly accurate in predicting measurements. Conceptually, it means that “new” theories seldom invalidate “old” theories. Instead, they provide a larger framework in which the “old” theory is an approximation which, in some circumstances (presumably those under which experiments were done until the new theory was found to be needed) produces accurate predictions. Thus Einstein’s theory of relativity, revolutionary in many senses, does not invalidate Newtonian physics. Instead, in situations in which all objects are moving at speeds small compared to the speed of light, it predicts that the results of a Newtonian analysis will describe physics well.

The Class:

This class is directed towards students who know very little astronomy or physics, but are interested in knowing more. We will assume that you are comfortable with mathematics at the level of algebraic manipulation of equations, and that you have had some contact with physics. To the extent possible, we will introduce any physics concept or mathematical technique we use that goes beyond this background. The science of the Universe, not surprisingly, encompasses a lot of physics, so anything you know about physics will probably be useful at some point in the class, and the more you know the more you will get out of it.

Our main goal is to give you a sense of how incredibly fun it is to be able to make sense of our Universe in the sense we described below. So we will try to give you the tools to make calculations, and then present the astrophysical phenomena to which they apply and invite you to try to study them with the tools you have acquired. One of the fun things about physics is that it is “right there in front of you.” Wherever possible, we will take the time to point out how what we are learning can help you make sense of everyday phenomena as well as more esoteric astrophysical ones.

Like the way science develops, our study of the Universe will proceed incrementally as a sequence of increasingly accurate approximations to the best modern science has to offer. Thus we will sometimes say things that are not precise, in the interest of making a pedagogical point. We will try to avoid saying things that are wrong. The historical development of our understanding is an exciting topic on its own; when a pedagogically sound approach parallels historical development we will follow history, but at other times we will forego historical accuracy for clarity. This is not a class on the history of science, and even when we mention historical developments this will be as brief remarks, with no attempt at completeness or absolute accuracy. Like our current understanding of the Universe, the end of this class is not ultimate truth. There will be statements we will never make quite precise, because stating them precisely requires more background than we use here.

Our main interest is in the interplay between fundamental physics and astronomy. Some very exciting aspects of astronomy - notably the question of the origins of life on Earth and the possibility of its existence elsewhere - will be mentioned in passing if at all.

The Process:

The material will be presented in video clips, about 2-3 hours of video a week. As far as possible these will be broken up into short segments. Longer clips can be viewed in separate pieces as your schedule allows. The videos will present material in a lecture format, using animations, simulations, and actual physical demonstrations to illustrate the concepts being discussed. Short quizzes will be embedded into the video clips to help you verify that you are following the discussion.

There will be two homework assignments every week. The main purpose of these is to help you deepen your understanding of the material. We believe you will find that after working with the concepts you will have a better grasp of what they mean and how they are used, as well as a better appreciation of their power - and yours. Even if you have no interest in such credit as this class offers, we urge you to take the time to work the assignments.

Grades in the class, for those interested, will be completely based on performance on the homework assignments. There will be no exams beyond this. Detailed grading policies are discussed in the Grading Policy link.

Experience shows that one of the best parts of student experience in these online courses comes from participation in the forum discussions. Interacting with a large, diverse group of students working through the same material as you can be rewarding as well as helping you learn things at a deeper level. Students should conduct themselves on the discussion forum boards as they would in any professional environment, with respect towards their fellow students, the class TAs, and the instructor. Constructive criticism is a welcome and valued part of scientific and educational discussion; flame wars and verbal abuse are not. Inappropriate posts and comments will be removed and repeat offenders will be banned from this course. The opportunity for cooperative learning through Coursera is tremendous, and we hope you will take advantage not only of other students' feedback and insight, but also contribute your own feedback where you can.

One important aspect of an Astronomy class that we cannot offer here is the opportunity for guided observation of the night sky. Seeing the objects we study through a small telescope outdoors makes the subject real. If you have access to a local observatory, we think that this will greatly enhance your experience in the class. The forum “Observation Notes” is a place to post about your experiences observing and read what others have done. The opportunity to compare notes across the globe is a wonderful feature of this class and we hope you will take advantage of it.

Another fun part of an Astronomy class is that the field is alive and active. There will be new and exciting developments during our nine weeks together - and we will be able to understand many of them and relate them to what we are learning. The forum “Current Astronomy Events” is a place to post about new discoveries and results.

This is our first time offering such a large, online course, and we're excited to see what works and interested to know how the course might be improved! Coursera itself is still young and developing and will probably experience some changes even during our course this winter. There will naturally be some rough edges, but we hope you will look on this as an opportunity not only to learn about astronomy, but also to help shape the fate of online education!

We are aware that the students for this class are located across the world. Therefore, there is a wide range of cultures, languages, ages, accessibility, time zones, interest levels, experience with the subject matter, etc..., and we aim to be as considerate of those differences as possible. The instructor and TAs naturally have their own backgrounds, and may not always be conscious of your paradigms. If there is some source of difficulty that we haven't anticipated, please be patient and bring the concern to our attention with a new discussion forum thread with a clear, specific title. The forum "General Course Feedback" is most appropriate for questions about clarity of the class materials and policies. The "Technical Issues" forum is most appropriate for difficulties using the website, problems with accessibility, or other technical problems.

The class teaching assistants (TAs) will be regularly monitoring the discussion forums and keep Ronen apprised of issues of concern to a significant portion of the class. The TAs will also attempt to directly respond to some posts in order to facilitate discussion or address certain problems. Please be aware that the TAs are neither professional experts in computer science, linguistics, sociology, history, astronomy nor are they full-time Coursera-employed staff. TA posts and comments don't necessarily represent the views of Ronen, Duke University, or Coursera.

The majority of important information for the class as a whole will come in two forms: class-wide emails and announcements posted to the Home page. Please check both regularly to keep in touch with class deadlines and current issues.

To communicate with us, please use the discussion forums. Please do not attempt to contact us directly outside the class. Such communication will receive no response. This is simply a matter of numbers: there are many thousands of students in the class and entering into personal communication with all of them is impossible.

Ronen Plesser, Duke University